Good luck with that. When a derelict Pershing 1A kit arrived unannounced on my doorstep a few years ago, I took it as an opportunity to draw and cut some balsa and ply alternatives to the original vac form fin parts. You can read about that process here:

https://www.rocketryforum.com/threa...9/#post-1855087

A PDF of the file is attached to that page. If you have access to a laser cutter you can cut your own set from that file. The final result will be far better than the original vacform fins.

James